A valve assembly such as this is mounted within or adjacent a tank to avoid damage when a conduit connected to the tank is damaged by impact. Such valve assemblies are commonly used, and often required by law, on road tankers where the risk of collision damage to conduits connected to the tank is high and on storage tanks having connected conduits in exposed conditions. By arranging a valve assembly in this way, and providing self-closing means, the valve assembly and the sealing of the tank are unaffected by damage occuring outboard of the tank.
Known valve assemblies provided for this purpose often employ a poppet valve or "inverted mushroom" sealing element with the stem of the sealing element projecting into the tank and surrounded by a superstructure carrying a spring to keep the sealing element seated. Actuation has been by means of a cable pulling from within the tank or a lever mechanism pushing from outside the tank and unattached to the sealing element. One of the reasons a sealing element such as this is commonly used is that where the tank has to be filled through the valve assembly and it is necessary to minimize spray and splashing within the tank, the poppet valve or inverted mushroom head helps to reduce spray. This spray can be highly dangerous, particularly with petroleum fluids, as it helps to create static electricity charges. Suitable deflectors must therefore be provided to inhibit the formation of this spray.
This form of construction is expensive, the superstructure carrying the spring is inaccessible inside the tank, and additional clearance space is required outside the tank for assembly and disassembly of the valve assembly.